"The target was the army shuttle bus. These recruits were travelling to the capital, Kabul, for their training. All of them were young."

Ahsanullah Shinwari, head of the Jalalabad hospital, said on Monday that all 12 bodies were brought to the hospital in the city, 125km from Kabul.

He said that the rest of the 38 wounded were in a critical condition.

The attacker was on a motorcycle when he rammed the bus, detonating explosives, according to Ahmad Ali Hazrat, chief of the Nangarhar provincial council.

The Taliban claimed responsibility for the attack.

In another incident early on Monday, a bomb hit a minibus carrying Afghan education ministry workers in Kabul, killing at least two people and wounding seven others.

The roadside bomb blew up as the bus was carrying workers to their offices in the Afghan capital's eastern Bagrami district, the ministry said.

There was no immediate claim of responsibility this attack.

Afghanistan's precarious security was underlined late on Saturday when at least two rockets hit the diplomatic zone in Kabul only hours after US Secretary of State John Kerry had held meetings with government leaders. No injuries were reported in those attacks.

Government workers and members of the security forces are often targeted by armed groups, including the Taliban, who are seeking to topple the US-backed government in Kabul.